Using USGS Stream-Flow Data to Develop Quantitative Skills in Introductory-Level
Geology Classes - Teaching Notes
Based on a pre-lab assignment (or introductory lecture), students should know:
1. Stream discharge and stage (elevation of flow)
2. Hydrographs
3. Flood records from New York
1. Flood records (pre-lab review) and recurrence interval – using the laptop and computer
projector, show students the compiled flood records in the Excel spreadsheet.
a. Floods on rivers can be viewed on a variety of time scales (e.g., daily, weekly,
seasonal, annual, etc.); note that records of peak annual flow are given in the data
table, and can be used for predicting the recurrence interval of floods, commonly
referred to as, e.g., “10-year flood”, “100-year flood”, etc. How can one
determine the recurrence interval of a flood of a given magnitude?
b. For each flood, the discharge, stage and rank (1 = highest magnitude) are given.
The recurrence interval can be determined from:
R = ___(N + 1)___
m
Where R=recurrence interval, N=total number of floods on record, m=flood rank
Show students how to enter this equation into the “Recurrence Interval” column in the spreadsheet.
3. Plotting discharge (Q) vs. recurrence interval (R) and a rating curve (Q vs. stage) – using the
Wellsville data, demonstrate how to graph Q vs. R in Excel. Use an X-Y scatter plot, format the x-axis
to a logarithmic scale, and apply a logarithmic best-fit line. Give the graph a title and label the axes in
Excel. This will give students a chance to see the steps they will perform before doing them in groups.
Q vs. R, Portageville
100,000
90,000
Equation of best-fit line:
y = 11975Ln(x) + 12297
R2 = 0.942
80,000
Estimated Q100 = 68000 cfs
Discharge (cfs)
70,000
60,000
50,000
40,000
30,000
20,000
10,000
0
1.00
10.00
100.00
Recurrence Interval (years)
1
Discharge vs Stage, Portageville Gauging Station, New York
100,000
Equation for best-fit line:
y = 6E-44e0.0997x
R2 = 0.8549
90,000
80,000
Estimated Q100 = 68000 cfs
Discharge (cfs)
70,000
60,000
50,000
40,000
30,000
20,000
Estimated Stage100
at Portageville = 1109 ft
10,000
0
1085
1090
1095
1100
1105
1110
1115
River Stage (ft asl)
4. Estimating the 100-year flood stage at Belfast – using the elevation profile of the Genesee River
between Wellsville and Portageville (plotted in Excel and given as a handout), students will plot the
estimated 100-year flood stage at the two locations and interpolate the 100-year flood stage at Belfast.
Elevation profile along the Genesee River, Wellsville to Portageville, New York
1600
1500
Wellsville gaging station
Elevation (ft asl)
1400
Estimated Stage100 at Belfast, ~1320 ft
1300
Belfast
1200
Portageville
gaging station
1100
1000
0
10
20
30
40
50
60
Distance (miles)
2
5. Establishing a flood-hazard zone for Belfast – using the topographic map of the town of Belfast,
NY, students will establish a flood-hazard zone based on the estimated stage of the 100-year flood on
the Genesee near the town (which they will determine in part 3 of the lab). They will shade in the area
on the map below the estimated stage.
5. To hand in - each GROUP (not individual) should hand in a copy of each of the four graphs (Q vs. R,
Q vs. stage for each gauging station), a copy of the stream elevation profile with the 100-year flood
stage plotted on it, a copy of the Belfast map showing the flood hazard zone, and answers to the
questions at the end of the lab. Students should check their graphs against the answer key before
printing them. They can check all their answers and their flood hazard-zone map at the end of lab.
3